diff --git a/CHANGELOG.md b/CHANGELOG.md
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--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,11 @@
+# Changelog for `yaftee-conduit-bytestring-ft`
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to the
+[Haskell Package Versioning Policy](https://pvp.haskell.org/).
+
+## Unreleased
+
+## 0.1.0.0 - YYYY-MM-DD
diff --git a/LICENSE b/LICENSE
new file mode 100644
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,26 @@
+Copyright 2025 Yoshikuni Jujo
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+1.  Redistributions of source code must retain the above copyright notice, this
+    list of conditions and the following disclaimer.
+
+2.  Redistributions in binary form must reproduce the above copyright notice,
+    this list of conditions and the following disclaimer in the documentation
+    and/or other materials provided with the distribution.
+
+3.  Neither the name of the copyright holder nor the names of its contributors
+    may be used to endorse or promote products derived from this software
+    without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/README.md b/README.md
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--- /dev/null
+++ b/README.md
@@ -0,0 +1,3 @@
+# yaftee-conduit-bytestring-ft
+
+Finger tree-based byte string tools for Yaftee Conduit.
diff --git a/Setup.hs b/Setup.hs
new file mode 100644
--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/src/Control/Monad/Yaftee/Pipe/ByteString/FingerTree/Crc32.hs b/src/Control/Monad/Yaftee/Pipe/ByteString/FingerTree/Crc32.hs
new file mode 100644
--- /dev/null
+++ b/src/Control/Monad/Yaftee/Pipe/ByteString/FingerTree/Crc32.hs
@@ -0,0 +1,66 @@
+{-# LANGUAGE ImportQualifiedPost #-}
+{-# LANGUAGE BlockArguments, LambdaCase #-}
+{-# LANGUAGE ExplicitForAll #-}
+{-# LANGUAGE RequiredTypeArguments #-}
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# OPTIONS_GHC -Wall -fno-warn-tabs #-}
+
+module Control.Monad.Yaftee.Pipe.ByteString.FingerTree.Crc32 (
+
+	run, reset, complement, crc32, crc32',
+
+	step
+
+	) where
+
+import Control.Monad.Fix
+import Control.Monad.Yaftee.Eff qualified as Eff
+import Control.Monad.Yaftee.Pipe qualified as Pipe
+import Control.Monad.Yaftee.State qualified as State
+import Control.HigherOpenUnion qualified as U
+import Data.HigherFunctor qualified as HFunctor
+import Data.Word.Crc32 qualified as Crc32
+import Data.ByteString.FingerTree qualified as BSF
+
+run :: forall nm es i o r . HFunctor.Loose (U.U es) =>
+	Eff.E (State.Named nm Crc32.C ': es) i o r -> Eff.E es i o (r, Crc32.C)
+run = (`State.runN` Crc32.initial)
+
+reset :: forall nm -> U.Member (State.Named nm Crc32.C) es => Eff.E es i o ()
+reset nm = State.putN nm Crc32.initial
+
+complement ::
+	forall nm -> U.Member (State.Named nm Crc32.C) es => Eff.E es i o ()
+complement nm = State.modifyN nm Crc32.complement
+
+crc32 :: forall nm ->
+	(U.Member Pipe.P es, U.Member (State.Named nm Crc32.C) es) =>
+	Eff.E es BSF.ByteString BSF.ByteString r
+crc32 nm = State.putN nm Crc32.initial >> body nm
+
+body :: forall nm ->
+	(U.Member Pipe.P es, U.Member (State.Named nm Crc32.C) es) =>
+	Eff.E es BSF.ByteString BSF.ByteString r
+body nm = fix \go -> Pipe.await >>= \s -> do
+	State.modifyN nm (`step` s)
+	Pipe.yield s
+	go
+
+crc32' :: forall nm ->
+	(U.Member Pipe.P es, U.Member (State.Named nm Crc32.C) es) =>
+	Eff.E es BSF.ByteString BSF.ByteString ()
+crc32' nm = State.putN nm Crc32.initial >> body' nm
+
+body' :: forall nm ->
+	(U.Member Pipe.P es, U.Member (State.Named nm Crc32.C) es) =>
+	Eff.E es BSF.ByteString BSF.ByteString ()
+body' nm = fix \go -> Pipe.awaitMaybe >>= \case
+	Nothing -> pure ()
+	Just s -> do
+		State.modifyN nm (`step` s)
+		Pipe.yield s
+		go
+
+step :: Crc32.C -> BSF.ByteString -> Crc32.C
+step = BSF.foldl' Crc32.step
diff --git a/src/Control/Monad/Yaftee/Pipe/ByteString/FingerTree/OnDemand.hs b/src/Control/Monad/Yaftee/Pipe/ByteString/FingerTree/OnDemand.hs
new file mode 100644
--- /dev/null
+++ b/src/Control/Monad/Yaftee/Pipe/ByteString/FingerTree/OnDemand.hs
@@ -0,0 +1,125 @@
+{-# LANGUAGE ImportQualifiedPost #-}
+{-# LANGUAGE BlockArguments, LambdaCase, OverloadedStrings #-}
+{-# LANGUAGE ScopedTypeVariables, TypeApplications #-}
+{-# LANGUAGE RequiredTypeArguments #-}
+{-# LANGUAGE DataKinds, ConstraintKinds #-}
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE ViewPatterns #-}
+{-# OPTIONS_GHC -Wall -fno-warn-tabs #-}
+
+module Control.Monad.Yaftee.Pipe.ByteString.FingerTree.OnDemand (
+
+	-- * RUN
+
+	run, States,
+
+	-- * ON DEMAND
+
+	onDemand, onDemandWithInitial, Members, Request(..), ByteString
+
+	) where
+
+import Control.Monad.Fix
+import Control.Monad.Yaftee.Eff qualified as Eff
+import Control.Monad.Yaftee.Pipe qualified as Pipe
+import Control.Monad.Yaftee.State qualified as State
+import Control.Monad.Yaftee.Except qualified as Except
+import Control.HigherOpenUnion qualified as U
+import Data.TypeLevel.List
+import Data.HigherFunctor qualified as HFunctor
+import Data.Bool
+import Data.ByteString.FingerTree qualified as BSF
+
+run :: forall nm es i o a . HFunctor.Loose (U.U es) =>
+	Eff.E (States nm `Append` es) i o a ->
+	Eff.E es i o ((a, Request), ByteString)
+run = (flip (State.runN @nm) $ ByteString BSF.Empty)
+	. (flip (State.runN @nm) $ RequestBuffer 100)
+
+type States nm = '[State.Named nm Request, State.Named nm ByteString]
+
+onDemand :: forall nm -> (
+	U.Member Pipe.P es,
+	Members nm es, U.Member (Except.E String) es ) =>
+	Eff.E es BSF.ByteString BSF.ByteString r
+onDemand nm = fix \go -> State.getN nm >>= \case
+	RequestBytes ln -> takeBytes nm ln
+		>>= maybe (Except.throw errne) ((>> go) . Pipe.yield)
+	RequestBuffer ln -> takeBuffer nm ln
+		>>= maybe (Except.throw errne) ((>> go) . Pipe.yield)
+	RequestString -> takeString nm
+		>>= maybe (Except.throw errne) ((>> go) . Pipe.yield)
+	RequestPushBack bs ->
+		State.modifyN nm (ByteString . (bs `BSF.append`) . unByteString) >>
+		Pipe.yield "" >> go
+	where
+	errne :: String
+	errne = "Not enough ByteString"
+
+onDemandWithInitial :: forall nm -> (
+	U.Member Pipe.P es,
+	Members nm es, U.Member (Except.E String) es ) =>
+	BSF.ByteString -> Eff.E es BSF.ByteString BSF.ByteString r
+onDemandWithInitial nm ib = do
+	State.putN nm $ ByteString ib
+	onDemand nm
+
+type Members nm es = (
+	U.Member (State.Named nm Request) es,
+	U.Member (State.Named nm ByteString) es )
+
+data Request
+	= RequestBytes Int
+	| RequestBuffer Int
+	| RequestString
+	| RequestPushBack BSF.ByteString
+	deriving Show
+
+newtype ByteString = ByteString { unByteString :: BSF.ByteString } deriving Show
+
+takeBytes :: forall nm -> (
+	U.Member Pipe.P es,
+	U.Member (State.Named nm ByteString) es ) =>
+	Int -> Eff.E es BSF.ByteString o (Maybe BSF.ByteString)
+takeBytes nm ln = State.getsN nm unByteString >>= \bs ->
+	case BSF.splitAt' ln bs of
+		Nothing -> readMore nm >>= bool (pure Nothing) (takeBytes nm ln)
+		Just (t, d) -> Just t <$ State.putN nm (ByteString d)
+
+takeBuffer :: forall nm -> (
+	U.Member Pipe.P es,
+	U.Member (State.Named nm ByteString) es ) =>
+	Int -> Eff.E es BSF.ByteString o (Maybe BSF.ByteString)
+takeBuffer nm ln = State.getsN nm unByteString >>= \bs ->
+	case BSF.splitAt' ln bs of
+		Nothing -> readMore nm >>= bool
+			(bool	(Just bs
+					<$ State.putN nm (ByteString BSF.Empty))
+				(pure Nothing) (BSF.null bs))
+			(takeBuffer nm ln)
+		Just (t, d) -> Just t <$ State.putN nm (ByteString d)
+
+takeString ::
+	forall nm ->
+	(U.Member Pipe.P es, U.Member (State.Named nm ByteString) es) =>
+	Eff.E es BSF.ByteString o (Maybe BSF.ByteString)
+takeString nm = State.getsN nm unByteString >>= \bs ->
+	case splitString bs of
+		Nothing -> readMore nm >>= bool (pure Nothing) (takeString nm)
+		Just (t, d) -> Just t <$ State.putN nm (ByteString d)
+
+splitString :: BSF.ByteString -> Maybe (BSF.ByteString, BSF.ByteString)
+splitString bs = case BSF.span (/= 0) bs of
+	(_, "") -> Nothing
+	(t, BSF.uncons -> Just (z, d)) -> Just (BSF.snoc t z, d)
+	_ -> error "Never occur"
+
+readMore :: forall nm -> (
+	U.Member Pipe.P es,
+	U.Member (State.Named nm ByteString) es ) =>
+	Eff.E es BSF.ByteString o Bool
+readMore nm = Pipe.awaitMaybe >>= \case
+	Nothing -> pure False
+	Just bs -> True <$ State.modifyN nm
+		(ByteString . (`BSF.append` bs) . unByteString)
diff --git a/test/Spec.hs b/test/Spec.hs
new file mode 100644
--- /dev/null
+++ b/test/Spec.hs
@@ -0,0 +1,2 @@
+main :: IO ()
+main = putStrLn "Test suite not yet implemented"
diff --git a/yaftee-conduit-bytestring-ft.cabal b/yaftee-conduit-bytestring-ft.cabal
new file mode 100644
--- /dev/null
+++ b/yaftee-conduit-bytestring-ft.cabal
@@ -0,0 +1,71 @@
+cabal-version: 2.2
+
+-- This file has been generated from package.yaml by hpack version 0.38.1.
+--
+-- see: https://github.com/sol/hpack
+
+name:           yaftee-conduit-bytestring-ft
+version:        0.1.0.0
+synopsis:       Finger tree-based byte string tools for Yaftee Conduit
+description:    Please see the README on GitHub at <https://github.com/YoshikuniJujo/yaftee-conduit-bytestring-ft#readme>
+category:       Control
+homepage:       https://github.com/YoshikuniJujo/yaftee-conduit-bytestring-ft#readme
+bug-reports:    https://github.com/YoshikuniJujo/yaftee-conduit-bytestring-ft/issues
+author:         Yoshikuni Jujo
+maintainer:     yoshikuni.jujo@gmail.com
+copyright:      (c) 2025 Yoshikuni Jujo
+license:        BSD-3-Clause
+license-file:   LICENSE
+build-type:     Simple
+extra-source-files:
+    README.md
+extra-doc-files:
+    CHANGELOG.md
+
+source-repository head
+  type: git
+  location: https://github.com/YoshikuniJujo/yaftee-conduit-bytestring-ft
+
+library
+  exposed-modules:
+      Control.Monad.Yaftee.Pipe.ByteString.FingerTree.Crc32
+      Control.Monad.Yaftee.Pipe.ByteString.FingerTree.OnDemand
+  other-modules:
+      Paths_yaftee_conduit_bytestring_ft
+  autogen-modules:
+      Paths_yaftee_conduit_bytestring_ft
+  hs-source-dirs:
+      src
+  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-export-lists -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints
+  build-depends:
+      base >=4.7 && <5
+    , bytestring-ft ==0.1.*
+    , higher-order-open-union ==0.1.*
+    , tools-yj ==0.1.*
+    , typelevel-tools-yj ==0.1.*
+    , yaftee ==0.1.*
+    , yaftee-basic-monads ==0.1.*
+    , yaftee-conduit ==0.1.*
+  default-language: Haskell2010
+
+test-suite yaftee-conduit-bytestring-ft-test
+  type: exitcode-stdio-1.0
+  main-is: Spec.hs
+  other-modules:
+      Paths_yaftee_conduit_bytestring_ft
+  autogen-modules:
+      Paths_yaftee_conduit_bytestring_ft
+  hs-source-dirs:
+      test
+  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-export-lists -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints -threaded -rtsopts -with-rtsopts=-N
+  build-depends:
+      base >=4.7 && <5
+    , bytestring-ft ==0.1.*
+    , higher-order-open-union ==0.1.*
+    , tools-yj ==0.1.*
+    , typelevel-tools-yj ==0.1.*
+    , yaftee ==0.1.*
+    , yaftee-basic-monads ==0.1.*
+    , yaftee-conduit ==0.1.*
+    , yaftee-conduit-bytestring-ft
+  default-language: Haskell2010